tools/imximage: use 0x prefix in HAB Blocks line

The u-boot-ivt.img.log file contains 0x prefixes in the HAB Blocks line,
while the SPL.log does not. For consistency, and to make it easier to
extract and put into a .csf file for use with NXP's code signing tool,
add 0x prefixes here.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-by: Breno Lima <breno.lima@nxp.com>